1. Field of the Invention
The present invention relates to a self ballasted fluorescent lamp and a lighting fixture which supplies high frequency energy to the fluorescent lamp.
2. Description of Related Art
Circuits for driving fluorescent lamps which include noise prevention elements are well known. For example, an inductor can be connected in series between the AC power supply and a shaping circuit which rectifies the AC power, and a smoothing capacitor can be connected across the AC power supply between the AC power supply and the inductor. Hereinafter, this driving circuit will be referred to as "prior art 1". Such a noise prevention circuit limits the flow of high frequency energy from a high frequency generating circuit within the driving circuit for the fluorescent lamp into the commercial AC power supply. Moreover, the generation of higher harmonic components on the input current can be reduced by limiting the starting current by connecting an impedance, such as a resistance, in series with the smoothing capacitor.
Japanese Provisional Publication No.5-174986 (hereinafter referred to as "prior art 2") discloses discharge lighting equipment which is also equipped with a smoothing circuit including a capacitor input system equipped with an electrolytic capacitor connected in parallel with a series connected noise prevention circuit and shaping circuit. In this discharge lighting equipment, the capacitance of the electrolytic capacitor is small so as to decrease the higher order harmonics generated by the high frequency source.
It has also become necessary to consider the influence of the higher order harmonics from the high frequency generator of a self ballasted fluorescent lamp on the commercial power supply. For an input power of about 35 W, an IEC (International Electrical Commission) standard requires that the 3rd harmonic component of the input current must be 86% or less of the fundamental component of the input current and the 5th harmonic must be 61% or less of the fundamental component of the input current.
Although prior art 1 discussed above includes an inductance for deterring high frequency noise and an impedance element for reducing the charging current of the smoothing capacitor and therefore, reducing higher harmonics, there is a problem that the higher harmonics cannot be controlled well enough in view of the size of the smoothing capacitor. Moreover, although prior art 2 includes a high frequency generator which can be used for a fluorescent lamp of about 40 W, since the number of parts and cost is greater than other designs, applying this design to self ballasted fluorescent lamps of not more than 35 W is difficult in commercial practice.